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Strengthening Blood Vessels

After an injury, the coagulation cascade goes into action to repair damaged tissue. When coagulation factors are eliminated in mouse embryos, the embryos die at mid-gestation and display extensive bleeding. Whether this is a result of defective platelet function or vascular defects has been unclear. Griffin et al. (see the Perspective by Carmeliet) have addressed this question by examining the role of PAR1, a G protein-coupled receptor that binds to and is cleaved by thrombin, a serine-protease coagulation factor. PAR1 is shown to be an endothelial factor and is needed for normal vascular development and integrity.